Packaging in plastic film



Feb. 13, 1962 D. E. RUECKERT ETAL 3,020,686

PACKAGING IN PLASTIC FILM 4 Sheets-Sheet 1 Filed Sept. 9, 1955 Feb. 13, 1962 Filed Sept. 9, 1955 D. E. RUECKERT ETAL PACKAGING IN PLASTIC FILM 4 Sheets-Sheet 2 al 69 2J 6.,

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DEA/V PUE'CAE'PT CARL J. L//V INVENTORS BY Kad/? ATTORNEY Feb. 13, 1962 D. E` RUECKERT ET AL PACKAGING IN PLASTIC FILM Filed Sept. 9, 1955 4 Sheets-Sheet 3 HYDRAULIC PUMP l I rI-I'En 85 /07 L l ilu f l l l Trrn /l [lpg .97

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L I IK N. :ZL J7 DFA/V E PECA/ERT CARL l L//VD INVENTORS 'WK/{M} ATTORNEY Feb. 13, 1962 D. E. RUEcKl-:RT ET AL 3,020,686

PACKAGING 1N PLASTIC FILM Filed Sept. 9, 1955 4 Sheets-Sheet 4 DFA/V E /PUE C KER' CARL J. L//vo y INVENTORS ATTORNEY 3,020,686 PACKAGING IN PLASTIC FILM Dean E. Rueckert, Mokena, and Carl lfLind, Evanston,

Ill., assigner-s to Swift @t Company, Chicago, lil., a corporation of Illinois Filed Sept. 9, 1955, Ser. No. 533,490 11 Claims. (Cl. 53-22) The present invention relates to a method and apparatus for use in the packaging of product, particularly a iiaccid product such as meat, and to a package.

The continued increase in importance of self-service marketing has resulted in numerous efforts to produce a package to meet this need. The desirable characteristics of such a package include:

The package should hold an amount of product that makes a convenient size package for the average housewife;

The product should be substantially ready for use by the housewife; i.e., if it is normally sliced before use, the product in the package should be sliced;

The package should be transparent so that the purchaser can see exactly what is being obtained; l

The package should be neat in appearance and of such a nature as to most attractively display the product inside;

The package should have substantially all the air removed, and this condition should be maintained, which not only contributes to producing an attractive package but also aids in the keeping qualities of the product Vin the package; and

The expense of producing the package should be reduced to an absolute minimum.

There have been numerous efforts to produce packages meeting these qualifications, but in the main some qualitications have been compromised in order to meet others deemed to be the more important. For example, in some instances the desire to have perfectly gas-tight packages has led to the use of techniques, structures and materials that are more costly than others. Even though such an increase in cost may only be a fraction of a cent per package, this becomes very important when the volumes involved are taken into consideration. In other instances just the reverse has been true. The desire to reduce cost has resulted in procedures, materials and structures producing a high percentage of leakers, ones that were not gas tight.

rlhe principal object and advantage of the present invention is the production of a package incorporating to an exceptionally high degree all of these desirable characteristics.

A further object and advantage of the present invention is the provision of a method and apparatus that is equally adapted for small and for large volume operations. Meat is not produced solely in big plants that can afford and economically use high volume automatic machines, but much of it comes from small places or" business having a relatively limited volume which could neither afford nor justify a high production automatic machine. However, these small places of business have just as great a need for a machine with an output tailored to their needs which will reduce and make more economical the labor they have in producing their product. The present invention is equally suited for both. While the embodiment illustrated and described is particularly adapted for the smaller volume plant and is not fully automatic, it will be readily apparent to those skilled in the art that this machine is eminently adapted for incorporation into high output automatic machines.

lOne of the features of the present invention is that there need not be any premanufacturing of parts for the package. It a package stiffener is used, as hereinafter S Y gi Patented Feb. 13, 1962 described, this part will be preformed, butin many embodiments such a stitiener is not necessary or may not be desired. The remainder of the vpackage is all 'formed about the product at the time the packaging vis done. This contributes to they meeting of the desirable package characteristics previously mentioned. l

In dealing with meats, even such manufactured products as sausage, one is handling a product that varies substantially in size from one unit to the next. While `cojnceivably it is possible to trim each piece to be of an identical size, this is costly because the trimmingscannot be etiiciently utilized so as to bring the same monetary return as does the basic piece of meat. This increases the costs of operation and of necessity increases 'the amount for which the basic 'piece of meat must be sold' in order to compensate for the trimming loss. While it might be desirable to produce each piece'of meat of the same size, this is not presently feasible and as a result the meat must vary in size as 'it 'is packaged. The present invention permits wide variations in the sizes of product that can be packaged by a given machine while still producing a package having the desirable characteristics outlined. As a matter of fact, this ability to package various sizes is so great that a single machine is not limited to packaging only one kind of product, but various kinds of product having different sizes and shapes can be packaged on a single machine. Where the volumes are large it may be desirable to have a machine tailored 'to package only a single product, but this is not necessary, and in smaller lvolume operations Vthe capital investment for a machine can be justified by using the same machine to package a Wide range of products.

Additional objects and advantages will become apparent from the following description taken in conjunction with the drawings in which:

FIGURE l is an isometric view partially in section of an embodiment of the method and apparatus of the present invention;

FlGURE 2 is a vertical section through the embodiment illustrated in FIGURE l;

FIGURE 3 is a schematic drawing of the control system for the embodiment of FIGURES l and 2;

FIGURE 4 is an isometric view of a package; and

FIGURE 5 is a vertical section through the package Yof FIGURE 4 with the packaging materials per se being exaggerated in size in order to better illustrate the package.

The embodiment illustrated in FIGURE l includes a suitable frame generally 10 and a holder generally 11 formed in two separable parts, an upper part 12 and a lower part 13. Holder 11 has a well 14 therein to receive the product and packaging material.

The upper part of the holder 12 is attached to Aa plate 16 mounted on the piston rod 17 of a iiuid cylinder generally 1S. Holder 12 is spaced from plate 16 by an insulator 15. Fluid cylinder 18 is suitably mounted on frame 10 in a manner not shown. To form half of a perimetric sealing head the lower end of the upper holder 12 is roughened, as by knurling, at 19 and is heated by electric heating coils 20 surrounding the upper part of the holder 12. =As will be seen in FIGURE 2, the inner diameter of the upper part 12 is slightly greater than the inner diameter of the lower part 13. Immediately about the upper end of lower part 13 is a recess 22 to receive an annular ring 23. Preferably the annular ring is formed of a heat resistant elastic material such as a silicon rubber. Ring 23 is supported on pins 24 mounted for longitudinal movement through suitable bores in the lower part 13 and frame lll. The lower ends of pins 24 rest on a plate 25 supported by springs 26 held in place by cap screws 27 threaded into frame 10. Plate 25 is freeto move up and down on cap screws 27 except for the urging of springs 26. Pins 24 have a shoulder at 28 to match a reduction in size of the holes through which the pins slide in frame 16 so as to limit the upward movement of the pins. e lower part 13 of holder 11 is attached to frame through an insulator 29.

Immediately outside of ring 23 is a fixed member 39 which at its upper end comes to a thin edge 31, concentric with ring 23, which cooperates with the recessed seat 32 of upper part 12 to form a clipper to sever the plastic film about the periphery of the package. A second heater 33 about fixed member 30 provides heat for the bottom half of the perimetric sealing head as represented by ring 23.

A peripheral vacuum head 35, which, in the illustrated embodiment takes the form of an annular ring slightly larger in diameter than that of the sealing head, is positioned to surround the sealing head and clipper by a mounting means 36. Mounting means 36 is made up of an arm 37 and a pair of rockers 38 loosely supported on a shaft 39. A bore 41 in arm 37 communicates with the inner passageway 42 of vacuum head 35 and with a hose connection 43 whereby a vacuum may be applied to the head and to the plurality of small openings 44 around the inner side of the head.

A collar 46 pinned to shaft 39 is positioned between rockers 38 to prevent movement of the rockers longitudinally of the shaft. A spring 47 about shaft 39 has one end 48 engaged in a hole in shaft 39 while the other end 49 engages a hole in one of rockers 38. Shaft 39 has an ofset 51 to which is connected an actuating lever 52 by means of a pin 53. Pillow blocks 54 attached to frame 10 (in a manner not shown) support shaft 39 and permit the rotation thereof. A spring 55 has one end 56 looped under offset 51, while the other end engages pillow block 54 thereby urging offset 51 upwardly from the position illustrated in FIGURE l. At the opposite end of shaft 39 the shaft is bent to form a hold down arm 59. Actuating lever 52 may be connected to a suitable treadle not shown.

Immediately below vacuum head 35 forming a part of fixed member 30 is an annular resilient pad 61 and a corresponding resilient pad 62 is mounted in movable member 63 associated with the upper part of holder 12.

Movable member 63 is supported on three shouldered pins 65 which are attached to member 63. Pins 65 pass through suitable openings in plate 16 to permit the pins to move with respect to the plate and yet hold the movable member 63 centered about the upper part 12 of the holder. Three adjusting screws 66 threaded into connecting plate 67 rest on the upper ends of the three pins 65. A second set of three shouldered pins 68 pass through openings in connecting plate 67 and in plate 16 and are attached to a pressure head 69 in well 14. Three springs 71 bear against pressure head 69 and also against plate 16 to urge the pressure head downwardly. Centering pins 72 threaded into plate 16 hold the springs 71 in proper position. Under the urging of springs 71 the heads of pins 68 are held in contact with connecting plate 67 and connecting plate 67 correspondingly holds adjusting screws 66 in contact with the heads of pins 65. Three legs 73 on movable member 63 limit the distance to which the movable member can approach fixed member 30 and thus the pressure that is exerted on the resilient pads 61 and 62 by vacuum head 35.

A second pressure head 75 in well 14 is connected to a piston rod 76 of uid cylinder 77. Fluid cylinder 77 is attached to frame 10.

A film cutoff in the form of a shears is provided by an upper plate St) attached to insulator and a lower plate 81 attached to fixed member 30.

Referring to FlGURE 3, a hydraulic pump 85 provides the uid pressure for the two cylinders 18 and 77. The high pressure line 86 from pump 85 divides into two branches with one branch going through a high pressure pressure regulating valve 87 and the other branch going through a low pressure pressure regulating valve 83. Following low pressure regulating valve S8 is a solenoid actuated normally opened valve 89. Correspondingly, following high pressure regulating valve 87 is a normally closed solenoid actuated valve 9G. From each of valves 89 and 90 a line 91 leads to a four-way control valve 92 for cylinder 18. The return line 93 from the four-way valve 92 is connected to pump 85. From a point between low pressure regulating valve S3 and solenoid valve 89 a low pressure line 95 leads to a four-way solenoid actuated control valve 96 for cylinder 1'7. A return line 97 connects four-way valve 96 with pump 85.

A vacuum pump 98 provides the source of vacuum for vacuum head 35 and a solenoid actuated normally closed valve 99 is connected in line 106 between vacuum pump 93 and hose connection 43 on arm 37.

A timer motor 102 is used having five cams 103 through 107, respectively, with ve respective switches 109 through 113. Switch 109 is wired in parallel with the starting switch and the corresponding cam 193 is such as to close switch 169 for one revolution after that revolution has been started by the closing of starting switch 115. Switch 110 is wired in series with the source of power as represented by terminals 116 and with the solenoid of vacuum valve 99. Switch 111 is wired in series with the source of power and with the solenoid of the valve for the pressure head cylinder 77. Switch 112 is wired in series with the source of power and with the solenoid of the valve for the holder cylinder 18. Switch 113 is wired in series with the source of power and with the solenoids of valves 89 and 90, which solenoids are in parallel with each other. It will be remembered that valve 89 is a normally open valve while valve 90 is a normally closed valve.

A switch 117 connects heater 20 in series with the source of power and a switch 118 connects heater 33 in series with the source of power.

We employ for a packaging material a laminated plastic having one portion thereof a plastic that is readily heat scalable and another portion that is highly impervious to the passage of fluids. Such a laminate can be formed of a rubber hydrochloride plastic, commonly sold under the trademark Plioiilm and a polyvinylidene chloride plastic, commonly sold under the trademark Saran The rubber hydrochloride plastic is eminently suitable for heat sealing, while the polyvinylidene chloride plastic gives excellent gaseous impermeability.

In setting up the machine for operation, switches 117 and 118 are closed so as to energize heaters 20 and 33. While variations in heating temperatures may be employed, we have found it very satisfactory to heat the upper part of the holder 12 to a temperature of 200 F. and the lower part of the holder 13 to a temperature of F. It should be noted that the heating of the bottom not only speeds the sealing but it also preconditions the film during the package making process, so as to do a better job of forming the film about the product.

Vacuum pump 98 is turned on and we have generally employed about 29 inches of vacuum gauge pressure. This produces an actual vacuum within the package of approximately 15 to 2O inches which is adequate to obtain good packages. The hydraulic pump 85 is also energized. The low pressure valve 88 is adjusted so as to produce approximately seven pounds per square inch of pressure on the product in the well during the forming of the package when taking into consideration the size of cylinder 77 and of pressure member 75, although this amount will vary with the product packaged. yIt should not be suthciently large to deform the product. Springs 71 should be just suflicient to resist this pressure and hold pressure head 69 in place. The high pressure control valve 57 is adjusted sufficiently greater to drive the upper part of the holder 12 on down against the resistance of springs 26 and 71 during the final forming of the package.

spades@ The first step in forming the package lis to draw a sheet of film 120 across the top of well 14, the holder 11 having been opened at the end of the preceding cycle. The end of film 120 is drawn sufficiently by well 14so as to be under hold down arm S9 during the forming cycle. The iilm 120 is positioned with the rubber hydrochloride film upwardly and the polyvinylidene chloride laminate downwardly. The product 121 to be sealed inthe package is placed over vthe film and it may or may not, depending upon the operators inclination, be pushed down into the well 14. -If a package stifener 122 is used it is now placed over the product. The stiffener is of such a size as to just fit within the portion 'of the well 14 inside the upper part 12 of the holder. The center of the stiffener 122 may be cut out as illustrated in IFEGURE 5. While various materials might be used for this stiffener, we have utilized a modified polystyrene plastic to good advantage. In many embodiments the stiffener 122 may be dispensed with.

Actuating lever 52 Vis drawn downwardly to lower the vacuum head 35 to a position about the holder 11. Hold down arm 59 is at this time still extending upwardly in a position above the lower film 120. A second sheet of laminated plastic 123 is then drawn across the top of the product 121 and stifener 122, if used, with the rubber hydrochloride portion of the film being downwardly in this case. Thesecond lfilm 12,3 is drawn across under hold down arm S9. Actuating lever 52 is further drawn down to move hold down arm 59 into contact with the top of the second iilm 123 and retain it fin placeduring the subsequent operations. The cont-inuedmovement of shaft 39 necessary `to bring hold down arm 59 is permitted by the presence of spring 47. v

Starting button 115 is pressed to energize motor 102. As soon as the motor commences vto turn, cam 103 closes switch 109 to lock the motor yin for one` revolution of the cam shaft. Switch 112 closes to reposition four-way valve 92. The valve had been positioned so as to draw the piston within cylinder 1S to the upper end of its stroke. Valve 89 is a normally open valve and permitted low pressure to be continually supplied to valve 92 through pipe 91 to hold the piston in that position. With the repositioning of valve 92 in response to the closing of switch 112, this low pressure from valve 39 is applied to the upper end of cylinder 13 to drive the piston downwardly and to commerce the lowering of the upper part of the head 12 and the parts connected thereto. Switch 110 closes to energize the solenoid of vacuum valve 99 and apply a vacuum to the vacuum head 35. At about this time movable member 63 reaches the position where the resilient pads 61 and 62 contact vacuum head 3S to prevent leakage of the vacuum. Further travel of the movable member 63 is prevented by the contact of legs 73 with fixed member 30.

The films being pressed about the vacuum head y35 provide an effective seal of the space within the vacuum head so as to permit the vacuum to be drawn within the package through openings 4d. Further downward movement of piston rod 17 is prevented by the strength of springs 71 and the contact of the legs 73 with fixed member 30. Springs 71 are sufiiciently strong to more than offset the force applied by cylinder 18 when the low Apressure is supplied to the cylinder. `In the meantime switch 111 is closed to reposition four-way valve 96 and apply the upward .movement to piston rod 76 of cylinder 77. This presses the product between pressure members 69 and 75 so as to flatten the product and squeeze out any trapped air. After a sufiicient period to evacuate the product, switch 113 is closed to energize the solenoids of both valves 89 and 90. Valve 89 closes and valve 9i) opens to apply high pressure to cylinder 18 in place of the previous low pressure. The high pressure 1s more than sufiicient to Overcome the resistance of springs 71 and consequently the upper part of the holder 12 continues its downward movement. l

The films are pressed between the knurled end '19 of the upper part of holder 12 and the annular 'ring 23. The fihns are heated sufficiently from this contact to heat seal the two films to each other thus forming a perimetric seal about the product. The upper part of holder 12 continues its downward Imovement pressing annular ring 23 down against the resistance of springs 26 to bring the thin edge 31 of fixed member 39 into Contact with the recessed seat 32 of the upper part 12 of the holder to clip the film about the sealed area and inside of the vacuum head 35. yIn the meantime the two films were also clipped along the line of shear between the upper blade S0 and the lower blade 81.

Switch 113 is fle-energized to apply lov pressure to line 91 rather than high pressure and switch 112 is cieenergized to reposition four-way valve 92 to apply the low pressure to the lower end of cylinder 18 and drive the piston in the cylinder upwardly, raising the upper part 12 of the holder. The package which is pushed up from the well by pressure head 75 may then be removed from the well 14. Switch `111 opens to reposition valve 96 and lower pressure head 75. Switch was previously opened to shut off the vacuum at about the time the package was sealed and switch 109 is now opened to Stop motor 102 at the end of the cycle.

The resulting package is illustrated in FIGURES 4 and 5. The packages, as shown in these figures, are inverted from the position .in which they were produced in the apparatus of FGURES l and 2. yIt will be Vnoted that the size or' Lhe product is substantially smaller than the size of the stifener 122. The product could be increased in size up to the size of the stiiener or reduced `below that illustrated in FIGURES 4 and 5. With any of these variations a neat tight package is still obtained.

In the embodiment illustrated in FIGURES 4 and 5, vents are employed to speed the evacuation of the package, although in some embodiments these may be dispensed with. Such vents may take the form of ribs or tunnels 124. Either structure forms channels through which the air may be quickly evacuated.

The embodiment illustrated in FIGURES l and 2 employs a cylindrical well 14 and the other parts are shaped accordingly. Variousother shapes of wells can be used depending upon the product to be packaged. In any event, the vacuum head 35 has a central opening to t about the film and product holder. Various other modifications will be apparent to those skilled in the art. For example the cross-section of the vacuum head 35 need not be circular but could be oval or even rectangular. All such modincations are deemed to be a part of the invention to the extend that they are covered by the appended claims inasmuch as a description of the specific embodiment was merely for the purpose of complying with 35 U.S.C. 112 and should not be construed as imposing unnecessary limitations upon the claims. While the invention has been discussed in connection with the handling of a flaccid product such as meats, other products having entirely different physical characteristics may be handled. Solids such as bars of soap and liquids such as motor oil have been successfully packaged in accordance with the teachings of the present invention. In the latter case certainobvious modifications in procedure are taken.

We claim:

l. A device for preparing packages from portions of nlm and being filled with product of a given maximum size, said device including means `to hold two portions of film about opposite sides of the product with the film extending outwardly from said product, a peripheral vacuum head having an opening therethrough said opening being of a greater size than said product, means Vto position said headabout the product and at a level between the level of said opposite sides with the product within the opening and an area between the head and the product, and means to seal the two portions together in 7 the peripheral area between said product and the sides of the head.

2. A device for preparing packages from portions of film and being lled with product of a given maximum size, said device including means to hold two portions of film about opposite sides of the product with the film extending outwardly from said product, a peripheral vacuum head having an opening therethrough said opening being of a greater size than said product, means to position said head about the product and at a level between the level of said opposite sides with the product within the opening and an area between the head and the product, means to press the portions tightly against the head, and means to seal the two portions together in the peripheral area between said product and the sides of the head.

3. A device for preparing packages from portions of film and being filled with product of a given maximum size, said device including means to hold two portions of film about opposite sides of the product with the film extending outwardly from said product, a tube-like vacuum head defining a central opening therethrough said opening being of a greater size than said product, means to position said head about the product and at a level between the level of said opposite sides with the product within the opening and an area between the head and the product, resilient means outside of said portions concentrically aligned with said head, and means to press said resilient means against the outside of said portions and onto said head.

4. A device for preparing packages from sheets of film and being filled with product of a given maximum size, said device including means to hold two portions of film about opposite sides of the product with the film extending outwardly from said product, a peripheral vacuum head having an opening therethrough said opening being of a greater size than said product, means to position said head about the product and at a level between the level of said opposite sides with the product within the opening and an area between the head and the product, a sealing head toV apply pressure to the outsides of the film in the peripheral area between the vacuum head and the product to thereby form a perirnetric seal about the latter, means to clip the film along a line enclosing said product between said seal and said vacuum head, and power means connected to said sealing head and to Said clipipng means to sequentially bring said sealing head against said film and to clip said film.

5. A device for preparing packages from sheets of lm and being filled with product of a given maximum size, said device including a holder having a well therein 'of substantially said size whereby said product may be received therein, said holder being formed of separable parts for the insertion and removal of product therefrom, portions of said holder immediately surrounding said well forming a perimetric sealing head, a peripheral vacuum head surrounding said poltions and movable with respect to each of said parts whereby a sheet of film may be inserted in said holder both above and below said head, and means to press the sheets of film against said vacuum head.

6. A device for preparing packages from sheets of film and being filled with product of a given maximum size, said device including a holder having a well therein of substantially said size whereby said product may be received therein, said holder being formed of separable parts for the insertion and removal of product therefrom, portions of said holder immediately surrounding said well 4forming a perimetric sealing head, one of said portions being rough, means to heat said one portion, the corresponding portion of the other part being a heat resistant `resilient material, a peripheral vacuum head surrounding -said portions and movable with respect to each of said parts whereby a sheet of film. may be inserted in said holder both above and below said head, and means to press the sheets of lm against said vacuum head.

7. A device for preparing packages from sheets of film and being filled with product of a given maximum size, said device including a holder having a well therein of substantially said size whereby said product may be received therein, said holder being formed of separable parts for the insertion and removal of product therefrom, portions of said holder immediately surrounding said well forming a perimetric sealing head, a peripheral vacuum head surrounding said portions and movable with respect to each of said parts whereby a sheet of film may be inserted in said holder both above and below said head, means to pres the sheets of film against said vacuum head, and clipping means concentrically mounted on said holder between said portions and said vacuum head.

8. A device for preparing packages from sheets of film and being filled with product of a given maximum size, said device including a holder having a well therein of substantially said size whereby said product may be received therein, a pair of pressure heads in said well at opposite sides of said product and adapted to squeeze the product therebetween, said holder being formed of separable parts for the insertion and removal of product therefrom, portions of said holder immediately surrounding said well forming a perimetric sealing head, a peripheral vacuum head surrounding said portions and movable with respect to each of said parts whereby a sheet of film may be inserted in said holder both above and below said head, and means to press the sheets of lm against said vacuum head.

9. A device for preparing packages from sheets of film and being filled with product of a given maximum size, said device including a holder having a well therein of substantially said size whereby said product may be received therein, a pair of pressure heads in said well at opposite sides of said product and adapted to squeeze the product therebetwen, said holder being formed of separable parts for the insertion and removal of product therefrom, portions of said holder immediately surrounding said well forming a perimetric sealing head, one of said portions being rough, means to heat said one portion, the corresponding portion of the other part being a heat resistant resilient material, a peripheral vacuum head surrounding said portions and movable with respect to each of said parts whereby a sheet of film may be inserted in said holder both above and below said head, means to press the sheets of film against said vacuum head, and clipping means on said holder concentrically mounted between said portions and said vacuum head.

l0. The method of forming packages of product from sheets of film, including placing a sheet of film across one side of said product, placing across the opposite side of said product a bottom member including channels leading from its central portion to its outer edge and a second sheet of film, simultaneously applying a vacuum about the periphery of said product to a zone interior of said films while exposing the exterior of both said films to substantially atmospheric pressure with said channels allowing evacuation of the area between the bottom member and the product, and sealing the two films to each other about the periphery of said product on the area within said zone while maintaining said vacuum.

11. The method of forming packages of products from sheets of film, including placing a sheet of film across one side of said product, placing across the opposite side of said product a stiffener containing vent channels leading from its central portion to its outer edge, positioning a second sheet of film outside of said stiffener, applying a vacuum between said films along a line generally enclosing said stifener while exposing the exterior of both said films to atmospheric pressure with said channels allowing evacuation of the area beneath the product, and sealing the two films to each other on the area be- 9 tween said line and the edge of said stiffener while maintaining said vacuum.

References Cited in the le of this patent UNITED STATES PATENTS 2,078,314 Busche Apr. 27, 1937 2,155,445 Pttenger et a1. Apr. 25, 1939 2,302,846 Farmer et al. Nov. 24, 1942 2,400,390 Clunan May 14, 1946 2,452,174 Arnold Oct. 26, 1948 10 Ramsbottom et al Dec. 9, 1952 Bower Mar. 16, 1954 Campbell Apr. 27, 1954 Barnby et a1 Nov. 16, 1954 Campbell July 5, 1955 Prohaska Jan. 10, 1956 Stanton Sept. 2,5, 1956 Hensgen Feb. 5, 1957 Grimstead et a1 July 16, 1957 Hanford Nov. 25, 1958 

